Serotonin regulation in a rat model of exercise-induced chronic fatigue

This study investigated the mechanisms underlying regulation of the serotonin system in the rat brain during exercise-induced chronic fatigue. High-performance liquid chromatography-mass spectrometry (HPLC-MS) was performed to measure serum tryptophan of the fatigued rat. HPLC was conducted to measure 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in the frontal cortex and hippocampus. In addition, 5-HT_1A receptor and 5-HT transporter (5-HTT) mRNA expressions were measured at the same locations using real-time PCR. The results demonstrated a significant reduction in the serum tryptophan level in rats with exercise-induced chronic fatigue. Moreover, increased 5-HT and decreased 5-HIAA levels were detected in the frontal cortex and hippocampus, and these alterations were significant. Further, 5-HTT expression was significantly increased and 5-HT_1A receptor expression was significantly decreased. These results indicate that the 5-HT system plays an important role in the development of exercise-induced chronic fatigue. The 5-HT levels in different parts of the brain increased simultaneously, especially at synapses, and these alterations were associated with changes in 5-HTT and 5-HT_1A mRNA expressions.